This invention relates to a method of casting vehicle wheels such as aluminum wheels or the like.
As is disclosed in the Japanese Published Unexamined Patent Application No. 151344/Heisei 2 (1990), there is conventionally known a method of casting a vehicle wheel by using mold means which comprises a lower mold and an upper mold which together form a cavity for molding therein a disk portion of the vehicle wheel, and split molds which form a cavity for molding therein a rim portion of the vehicle wheel by enclosing the lower and the upper molds. In this method, the split molds are opened when a molten material in the cavities has been completely solidified and the lower and the upper molds are also opened to take out a product.
In this method, the external side of the vehicle wheel which faces an outside of a vehicle when mounted thereon is molded by the lower mold. Cooling water passages are provided in the lower mold and the lower mold is water-cooled by means of cooling water which flows through the passages. The solidification of the external side of the vehicle wheel is thus accelerated so that no defects, such as, shrinkage cavities, occur.
In case reinforcing ribs are formed on the internal side of the vehicle wheel, it is desirable, for the purpose of shortening the casting cycle time, to cool also the upper mold which forms the internal side of the vehicle wheel. However, if the molten material on the internal side is solidified more quickly than that on the external side, unsolidified molten material on the external side is pulled towards the internal side, thereby giving rise to shrinkage cavities on the external side. Therefore, no positive cooling of the upper mold is carried out in the present state of the art.